1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device, and more particularly, to an LCD device having a multi-domain structure.
2. Discussion of the Related Art
In general, an LCD device includes two substrates disposed to have their respective electrodes facing each other, and a liquid crystal layer is interposed between the respective electrodes. When a voltage is applied to the electrodes, an electric field is generated between the electrodes to modulate light transmittance of the liquid crystal layer by reorienting liquid crystal molecules, thereby displaying images.
There are many types of LCDs, one of which is an active matrix LCD (AM-LCD) that includes a matrix array of pixels, wherein each of the pixels in the AM-LCD has a thin film transistor (TFT) and a pixel electrode. The AM-LCD has high resolution and superiority in displaying moving images.
FIG. 1A is a schematic plan view of an array substrate for a LCD device according to the related art, and FIG. 1B is a schematic plan view of a color filter substrate for the LCD device of FIG. 1A. In FIG. 1A, a gate line 14 is formed along a first direction and a data line 24 is formed along a second direction perpendicular to the first direction. A pixel region “P” is defined by the crossing of the gate line 14 and the data line 24, a TFT “T” is connected to the gate line 14 and the data line 24, and a pixel electrode 28 is formed in the pixel region “P” and connected to the TFT “T.” The TFT “T” includes a gate electrode 12 that extends from the gate line 14, a source electrode 20 that extends from the data line 24, a drain electrode 22 that is spaced apart from the source electrode 20, and a semiconductor layer 18 that overlaps the source and drain electrodes 20 and 22. In addition, a first orientation film 30 is formed on the pixel electrode 28 to induce an initial alignment of a liquid crystal layer (not shown).
In FIG. 1B, a black matrix 52 is formed at a peripheral portion of the pixel region “P” and has an open portion corresponding to the pixel region “P.” In addition, a color filter layer 54 is formed in the pixel region “P” and includes red, green, and blue sub-color filters 54a, 54b, and 54c, wherein each of the sub-color filters 54a, 54b, and 54c corresponds to one pixel region “P.” Then, a common electrode 56 and a second orientation film 58 are sequentially formed on the color filter layer 54.
FIG. 2 is a schematic cross-sectional views, along II—II of FIGS. 1A and 1B, showing the LCD device according to the related art. In FIG. 2, first and second substrates 10 and 50 are spaced apart and face from each other, and a liquid crystal layer 70 is interposed between the first and second substrates 10 and 50. A first orientation film 30 is formed between the liquid crystal layer 70 and the first substrate 10, and a second orientation film 58 is formed between the liquid crystal layer 70 and the second substrate 50. The liquid crystal layer 70 has a twisted nematic (TN) mode, where liquid crystal molecules 72 have a 90° twisted structure without an applied voltage and are aligned orthogonal to the first and second substrates 10 and 50 with an applied voltage. The first and second orientation films 30 and 58 are rubbed along opposing directions.
When an electric field is induced to the liquid crystal layer 70, the liquid crystal molecules 72 in the pixel region “P” are aligned along one direction orthogonal to the first and second substrates 10 and 50. Thus, a first light beam “L1” controlled by a long axis of the liquid crystal molecules 72 and a second light beam “L2” controlled by a short axis of the liquid crystal molecules 72 are emitted according to a viewing angle. Since the first and second light beams “L1” and “L2” have different intensities, a user observes non-uniform brightness of the LCD device, thereby creating a narrow viewing angle.
In order to solve these problems, the LCD device is provided with a multi-domain structure where an alignment state of the liquid crystal molecules is symmetrically divided in each pixel region. The multi-domain structure for the TN mode LCD device is obtained by adjusting a rubbing direction of an orientation film or by distorting an electric field. In the multi-domain structure using a distorted electric field, an alignment state of the liquid crystal molecules is stabilized to the multi-domain structure by generating a fringe electric field.
FIG. 3A is a schematic plan view of an array substrate for an LCD device having a 2-domain structure according to the related art. FIG. 3B is a schematic plan view of a color filter substrate for the LCD device of FIG. 3A according to the related art. In FIG. 3A, a gate line 114 and a data line 124 cross each other, a TFT “T” is connected to the gate line 114 and the data line 124, and a pixel electrode 128 having a slit 127 is connected to the TFT “T.” In addition, an auxiliary electrode 113 is provided to overlap the slit 127, and the slit 127 is disposed along a diagonal direction of the pixel electrode 128. For example, the auxiliary electrode 113 is formed of the same material as the gate line 114 through the same process, and is electrically separated from the pixel electrode 128, but is connected to a common line 115. In addition, a first orientation film 130 is formed on the pixel electrode 128.
In FIG. 3B, a black matrix 152 is formed in a peripheral portion of the pixel region “P” and has an open portion corresponding to the pixel region “P.” In addition, a color filter layer 154 is formed in the pixel region “P” and includes red, green, and blue sub-color filters 154a, 154b, and 154c, wherein the red, green, and blue sub-color filters 154a, 154b, and 154c are alternately disposed in the pixel region “P.” Furthermore, a protrusive pattern 155 is formed in a boundary portion of the pixel region “P,” and a common electrode 156 and a second orientation film 158 are sequentially formed on the protrusive pattern 155.
In the LCD device of FIGS. 3A and 3B, the slit 127 of the pixel electrode 128, the auxiliary electrode 113, and the protrusive pattern 155 induce distortion of the electric field to form the 2-domain structure.
FIG. 4 is a schematic cross-sectional view, along IV-IV of FIGS. 3A and 3B showing the LCD having the 2-domain structure according to the related art. In FIG. 4, first and second substrates 110 and 150 are spaced apart from and face each other, and the auxiliary electrode 113 is formed on an inner surface of the first substrate 110 in a central portion of the pixel region “P.” Then a gate insulating layer 116 is formed on an entire surface of the first substrate 110. Accordingly, the data line 124 is formed on the gate insulating layer 116 at both sides of the pixel region “P,” and a passivation layer 126 is formed on the data line 124. Next, the pixel electrode 128 is formed on the passivation layer in the pixel region “P,” wherein the slit 127 corresponds to the auxiliary electrode 113.
Then, a black matrix 152 is formed on an inner surface of the second substrate 150 to correspond to the data line 124, a color filter layer 154 is formed on the black matrix 152, and a common electrode 156 is formed on the color filter layer 154. Next, a protrusive pattern 155 is formed on the common electrode 156 in a boundary portion of the pixel region “P,” and the second orientation film 158 is formed on the protrusive pattern 155 and the common electrode 156.
In FIG. 4, a liquid crystal layer 170 is formed between the first and second orientation films 130 and 158. Due to distortion of the electric field by the slit 127 of the pixel electrode 128, the auxiliary electrode 113, and the protrusive pattern 155, the liquid crystal layer 170 has 2 domains of different alignment states utilizing the slit 127 as a border. Since liquid crystal molecules 172 in the adjacent domains have symmetric alignment states, a viewing angle of the LCD device is improved.
However, since the LCD device is fabricated through an attachment process of the first substrate having array elements, such as a TFT, and the second substrate having the color filter layer and includes an injection process of the liquid crystal molecules, misalignment of the protrusive pattern with the boundary portion of the pixel region may occur during the attachment process. Since this misalignment causes light leakage, a sufficient attachment margin is necessary. That may be obtained by increasing a width of the black matrix. However, as the attachment margin increases, aperture ratio decreases. Moreover, since the protrusive pattern is formed through an additional process, a total number of individual fabricating steps increases and production costs also increase.